Vertically aligned liquid crystal display

ABSTRACT

Disclosed is a liquid crystal display comprising a first substrate made of an insulating material; pixel electrodes formed on the first substrate, the pixel electrodes having a first aperture pattern; a second substrate made of an insulating material and provided opposing the first substrate at a predetermined distance; a common electrode formed on the second substrate, the common electrode having a second aperture pattern; and a liquid crystal layer made of liquid crystal material that is injected between the first and second substrates, wherein either or both of the pixel electrodes and the common electrode include stepped portions that protrude a predetermined distance away from the substrates, between apertures of the first and/or second aperture patterns.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a vertically aligned liquid crystaldisplay, and more particularly, to a vertically aligned liquid crystaldisplay having a aperture pattern formed in electrodes to obtain a wideviewing angle.

(b) Description of the Related Art

A liquid crystal display (LCD) is structured having liquid crystalinjected between an upper substrate having a common electrode and acolor filter, and a lower substrate having thin film transistors andpixel electrodes. A voltage of a different potential is applied to thepixel electrodes and common electrode to form an electric field, therebyvarying the alignment of liquid crystal molecules of the liquid crystalmaterial. In this way, the transmittance of incident light is controlledto display images.

In a vertically aligned (VA) LCD, long axes of the liquid crystalmolecules align themselves vertically to the substrates in a state whereno electric field is formed between the substrates. The VALCD has a highcontrast ratio and a wide viewing angle such that this LCD configurationis the most commonly used type of liquid crystal display.

In one method to obtain a wide viewing angle in the VA LCD, aperturepatterns are formed in the electrodes. With this configuration, a fringefield is used to uniformly scatter a slanting direction of the liquidcrystal molecules into four directions to achieve a wide viewing angle.A conventional VA LCD, having aperture patterns formed in the electrodesto obtain a wide viewing angle, will now be described with reference toFIG. 1.

FIG. 1 shows a partial sectional view of a conventional VA LCD havingaperture patterns formed in electrodes.

A pixel electrode 110 is formed on an insulating lower substrate 100,and a common electrode 210 is formed on an insulating upper substrate200. Aperture patterns are formed in the pixel electrode 110 and thecommon electrode 210. Apertures of the aperture pattern of the pixelelectrode 110 are provided alternately with apertures of the aperturepattern of the common electrode 210. Further, liquid crystal material isinjected between the substrates 100 and 200 to form a liquid crystallayer 300.

As shown in the drawing, a fringe field generated by the aperturepatterns uniformly controls a slanting direction of liquid crystalmolecules of the liquid crystal layer 300. A wide viewing angle isrealized as a result. However, at center portions between apertures ofthe upper substrate 200 and the lower substrate 100, weak fringe fieldforms an area by the vertical electric field with respect to thesubstrates where the liquid crystal molecules do not quickly changealignments by the electrical field. Also, the liquid crystal moleculesin these areas begin to slant only after liquid crystal molecules in thevicinity of the aperture patterns are slanted. This slows down theresponse speed of the LCD.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve the aboveproblems.

It is an object of the present invention to provide a vertically alignedliquid crystal display in which a lower and an upper aperture patternare formed in electrodes of at least one substrate to form a steppedpattern at the center of the aperture pattern. Accordingly, a responsespeed is improved.

To achieve the above object, the present invention provides a liquidcrystal display comprising a first substrate made of an insulatingmaterial; pixel electrodes formed on the first substrate, the pixelelectrodes having a first aperture pattern; a second substrate made ofan insulating material and provided opposing the first substrate at apredetermined distance; a common electrode formed on the secondsubstrate, the common electrode having a second aperture pattern; and aliquid crystal layer made of liquid crystal material injected betweenthe first substrate and the second substrate, wherein either or both ofthe pixel electrodes and the common electrode include stepped portions,which protrude a predetermined distance away from the substrates,between apertures of the first and/or second aperture patterns.

According to a feature of the present invention, the pixel electrodesinclude the stepped portions.

According to another feature of the present invention, the steppedportions are formed by providing the pixel electrodes over a gateinsulation layer and a protection layer.

According to yet another feature of the present invention, the commonelectrode includes the stepped portions.

According to still yet another feature of the present invention, thepixel electrodes include first stepped portions and the common electrodeincludes second stepped portions.

According to still yet another feature of the present invention, thefirst stepped portions and the second stepped portions are provided in asequence of the first aperture pattern, the second stepped portions, thefirst stepped portions, and the second aperture pattern.

According to still yet another feature of the present invention, theliquid crystal display further comprises thin film transistors formed onthe first substrate, the thin film transistors switching image signalstransmitted to the pixel electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the invention,and, together with the description, serve to explain the principles ofthe invention:

FIG. 1 is a partial sectional view of a conventional vertically alignedliquid crystal display;

FIG. 2 is a partial sectional view of a vertically aligned liquidcrystal display according to a first preferred embodiment of the presentinvention;

FIG. 3 is a combination sectional view and transmissivity graphcomparing the vertically aligned liquid crystal display of the firstpreferred embodiment of the present invention with a conventionalvertically aligned liquid crystal display; and

FIG. 4 is a partial sectional view of a vertically aligned liquidcrystal display according to a second preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

FIG. 2 shows a partial sectional view of a vertically aligned liquidcrystal display according to a first preferred embodiment of the presentinvention.

A pixel electrode 11 is formed on a lower substrate 10, the lowersubstrate 10 being made of an insulating material such as glass, and acommon electrode 21 is formed on an upper substrate 20, which is alsomade of an insulating material. A first aperture pattern P1 and a secondaperture pattern P2 are formed respectively in the pixel electrode 11and the common electrode 21. Apertures of the first aperture pattern P1are provided alternately with apertures of the second aperture patternP2. Plateaus 14 are formed on the lower substrate 10. The pixelelectrode 11 is formed over the plateaus 14 such that stepped portionsare formed. The plateaus 14 are formed by a gate insulating layer 12 anda protection layer 13.

The stepped portions start at roughly a center between an edge A of theapertures of the first aperture pattern P1 and an edge B of theapertures of the second aperture pattern P2, that is at areas C. Since afringe field is also formed by the stepped portions, the liquid crystalmolecules positioned over areas C quickly respond to a generatedelectric field.

In a liquid crystal display, many more elements than those describedabove are provided on the lower and upper substrates 10 and 20. Forexample, additionally provided on the lower substrate 10 are gatewiring, data wiring, and thin film transistors, and additionallyprovided on the upper substrate 20 are a color filter and a blackmatrix. The gate wiring transmits scanning signals, the data wiringtransmits image signals, and the thin film transistors act as aswitching element to either transmit or cut off the image signals to thepixel electrode 11 according to the scanning signals. These elements donot appear in the drawing to simplify the explanation of the firstembodiment.

FIG. 3 shows a combined sectional view and transmissivity graphcomparing the vertically aligned liquid crystal display of the firstpreferred embodiment of the present invention with a conventionalvertically aligned liquid crystal display.

In FIG. 3, it is to be assumed that a drive voltage be applied after athreshold voltage of 1.7V is applied for 150 msec. Shapes ofequipotential lines and alignment of liquid crystal molecules are shownin the lower part of FIG. 3, while the curved lines of the upper part ofFIG. 3 are transmissivity curves, in which the changes are with respectto time.

As shown by area B of the conventional LCD, in which no stepped portionis provided, light transmissivity slowly decreases with time at areasbetween the apertures of the aperture patterns. On the other hand, inthe present invention having stepped portions, the liquid crystalmolecules at areas between the apertures of the aperture patterns arealigned simultaneously with the liquid crystal molecules at edges of theapertures as a result of the transformed electric field due to thestepped portions. Accordingly, with reference to area A, a lighttransmissivity is nearly identical throughout the liquid crystal displayof the present invention, thereby enhancing response speed.

Table 1 below shows a comparison between response speeds of theconventional LCD and the LCD of the present invention at different graylevels.

TABLE 1 Starting Applied Prior art Present Difference in voltage (V)voltage (V) (ms) invention (ms) time (ms) 1.7 2.5 147 123 24 3.0 80 6416 3.5 47 38 9 4.0 32 25 7 5.0 16 13 3 2.0 2.5 120 100 20 3.0 67 58 10Average 72.7 60.14 12.56

As shown in Table 1, the present invention has a response speed at allgray levels that is faster than the conventional LCD. Of particularinterest is the improvement in response speed of between 20 and 25 ms atlow gray levels.

FIG. 4 shows a partial sectional view of a vertically aligned liquidcrystal display according to a second preferred embodiment of thepresent invention.

A pixel electrode 11 is formed on a lower substrate 10, the lowersubstrate 10 being made of an insulating material such as glass, and acommon electrode 21 is formed on an upper substrate 20, which is alsomade of an insulating material. A first aperture pattern P1 and a secondaperture pattern P2 are formed respectively in the pixel electrode 11and the common electrode 21. Apertures of the first aperture pattern P1are provided alternatingly with apertures of the second aperture patternP2. Plateaus 14 are formed between the pixel electrode 11 and the lowersubstrate 10, and plateaus 22 are formed between the common electrode 21and the upper substrate 20. As a result, stepped portions are formed onthe lower and upper substrates 10 and 20. The plateaus 14 of the lowersubstrate 10 are formed of a gate insulating layer 12 and a protectionlayer 13.

The stepped portions of the lower substrate 10 and the upper substrates20 start at a center area between an edge A of the apertures of thefirst aperture pattern P1 and an edge B of the apertures of the secondaperture pattern P2. That is, areas C, at which point the steppedportions of the lower substrate 10 begin to form, are misaligned withareas D, at which point the stepped portions of the upper substrate 20begin to form.

By forming the stepped portions also on the upper substrate 20, thefurther increased effects of varying the electric field improve theresponse speed.

In the LCDs of the present invention described above, stepped portionsare formed only on the lower substrate and on both the upper and lowersubstrates. However, it is also possible to form protruding areas onlyon the upper substrate. A detailed description of such a configurationwill be omitted, as such modifications will be well known to one ofordinary skill in the art.

In the present invention, the response speed of the liquid crystaldisplay is improved by forming stepped portions between apertures of thelower substrate and the upper substrate. That is, by the transformedelectric field resulting from the stepped portions, the slantingdirection of the liquid crystal molecules is better controlled in areasbetween the apertures to enhance the overall response speed.

Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

What is claimed is:
 1. A liquid crystal display, comprising: a firstsubstrate made of an insulating material; pixel electrodes formed onsaid first substrate, said pixel electrodes having a first aperturepattern; a second substrate made of an insulating material and facingsaid first substrate at a predetermined distance; a common electrodeformed on said second substrate, said common electrode having a secondaperture pattern; and a liquid crystal layer made of liquid crystalmaterial injected between said first substrate and said secondsubstrate, wherein at least one of said pixel electrodes and said commonelectrode include a stepped portion, which protrudes a predetermineddistance away from the substrates, between the first aperture patternand the second aperture pattern.
 2. The liquid crystal display of claim1, wherein said pixel electrodes include the stepped portion.
 3. Theliquid crystal display of claim 2, wherein the stepped portion is formedby providing the pixel electrodes over a gate insulation layer and aprotection layer.
 4. The liquid crystal display of claim 1, wherein saidcommon electrode includes the stepped portion.
 5. The liquid crystaldisplay of claim 1, wherein said pixel electrodes include a firststepped portion and said common electrode includes a second steppedportion.
 6. The liquid crystal display of claim 5, wherein the firststepped portion and the second stepped portion are provided in asequence of the first aperture pattern, the second stepped portion, thefirst stepped portion, and the second aperture pattern.
 7. The liquidcrystal display of claim 1, further comprising a thin film transistorformed on said first substrate, the thin film transistor switching imagesignals